130 PHYSIOLOGY OF ALIMENTATION. 



The methods which have been devised for the quantitative 

 estimation of proteolytic ferments are various and still 

 exceedingly unsatisfactory. For the.most part, no absolute 

 but only comparative estimations of the ferment content of 

 any organ or secretion can be made. As with the other fer- 

 ments, it is not possible to obtain the proteolytic ferments in 

 anything even approximating a pure state without tremendous 

 and incalculable loss, so that direct estimations are out of the 

 question. * We have to content ourselves therefore with com- 

 parative studies, in which we can say a definite mixture 

 digests a chosen quantity of a protein more or less rapidly 

 than an arbitrarily established standard. From the degree 

 of difference we can get some idea of the relative amounts of 

 proteolytic ferment present in the different reaction tubes, but 

 this only within certain well-defined limits of time and limits 

 of concentration of ferment and protein. Of the various 

 methods and their modifications which have been devised 

 from time to time for the quantitative estimation of pro- 

 teolytic ferments, only those are mentioned of which an under- 

 standing is necessary for what is to follow in this volume. 



(a) Grutzner's 1 Method. This is a colorimetric method in 

 which fibrin from ox-blood is used. The fibrin obtained by 

 whipping fresh blood is finely chopped and washed in water, 

 after which it is stained in a carmine solution. After another 

 thorough washing in water this carmine-stained fibrin is pre- 

 served in glycerine. When a test is to be made the colored 

 fibrin is thoroughly washed in water and a weighed amount 

 introduced into each of the digestion mixtures to be tested. 

 As the fibrin is digested the reaction mixture is colored red, 

 from the depth of which, when compared with an arbitrarily 

 established scale, deductions can be made regarding the rela- 

 tive digestive power of the different mixtures. 



(b) Mett's Method consists in a determination of the amount 

 of coagulated egg albumin digested out of capillary tubes. 



1 GRUTZNER: PFLUGER'S Archiv, 1874, VIII, p. 452. 



